Focal Adhesion Kinase (FAK/PTK2) is a cytoplasmic tyrosine kinase that localizes to focal adhesions and regulates cell adhesion, migration, and survival. In the nervous system, FAK plays important roles in neuronal development, synaptic plasticity, and responses to injury. FAK has emerged as a key player in neurodegenerative disease pathogenesis, with alterations observed in Alzheimer's disease, Parkinson's disease, stroke, and traumatic brain injury[1].
FAK was originally discovered as a heavily tyrosine-phosphorylated protein in v-src transformed cells and has since been recognized as a central signaling hub at integrin-based adhesion sites. The protein is encoded by the PTK2 gene and is expressed in virtually all cell types, with particular importance in cells of the nervous system[2].
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|---|---|
| **Protein Name** | Protein Tyrosine Kinase 2 (Focal Adhesion Kinase) |
| **Gene Symbol** | [PTK2](/genes/ptk2) |
| **UniProt ID** | [Q05513](https://www.uniprot.org/uniprot/Q05513) |
| **Molecular Weight** | 119 kDa (1,052 amino acids) |
| **Subcellular Localization** | Focal adhesions, cytoplasm, nucleus |
| **Protein Family** | FAK family (non-receptor tyrosine kinases) |
| **PDB Structure** | [2J0J](https://www.ebi.ac.uk/pdbe/entry/pdb/2J0J), [4K9Y](https://www.ebi.ac.uk/pdbe-entry/pdb/4K9Y), [5AXN](https://www.ebi.ac.uk/pdbe/entry/pdb/5AXN) |
| **Brain Expression** | Neurons, astrocytes, microglia, endothelial cells |
| **Associated Diseases** | Alzheimer's disease, Parkinson's disease, stroke, TBI |
FAK is a 1,052 amino acid non-receptor tyrosine kinase that functions as a key regulator of cell-extracellular matrix interactions. The protein localizes to focal adhesions, which are specialized structures that connect the actin cytoskeleton to the extracellular matrix through integrin receptors. FAK transduces signals from the extracellular environment to the intracellular signaling network, influencing cell survival, proliferation, migration, and differentiation[3].
In the nervous system, FAK is critical for neuronal development, including migration, axon guidance, and synapse formation. In the adult brain, FAK continues to play important roles in synaptic plasticity, learning and memory, and responses to injury. Dysregulation of FAK signaling has been implicated in multiple neurodegenerative diseases, making it a potential therapeutic target[4].
FAK contains several distinct structural domains that mediate its diverse functions:
¶ N-Terminal FERM Domain (aa 1-400)
The FERM (Four.1-Ezrin-Radixin-Moesin) domain is a unique feature of FAK that mediates:
- Auto-inhibition of kinase activity through intramolecular interactions
- Binding to phosphatidylinositol 4,5-bisphosphate (PIP2)
- Interaction with integrin β subunits
- Docking for downstream signaling partners
- Nuclear localization signals
¶ Kinase Domain (aa 400-800)
The central catalytic domain contains:
- ATP-binding site (active in phosphorylated form)
- Tyrosine autophosphorylation sites (Y397, Y576, Y577)
- Activation loop regulatory motifs
- Substrate binding pocket
¶ Focal Adhesion Targeting (FAT) Domain (aa 900-1052)
The C-terminal FAT domain is essential for:
- Focal adhesion localization
- Binding to paxillin and other focal adhesion proteins
- Tethering to the actin cytoskeleton
- Dimerization and oligomerization
FAK contains multiple proline-rich regions that bind:
- Src family kinases (SH3 domain binding)
- CAS family proteins
- Other SH3-containing signaling proteins
FAK is a primary effector of integrin signaling:
- Activated by integrin clustering and engagement with ECM
- Autophosphorylates at Y397 creating Src family binding site
- Activates downstream pathways including Src, MAPK, PI3K/Akt, and Rho GTPases
- Coordinates cytoskeletal reorganization and adhesion dynamics
FAK undergoes extensive tyrosine phosphorylation:
- Y397: Autophosphorylation site, creates Src SH2 binding site
- Y576/Y577: Full kinase activation
- Y861: Focal adhesion turnover
- Y925: Grb2/SOS recruitment, MAPK activation
FAK controls cytoskeletal dynamics through:
- Modulation of actin polymerization
- Regulation of focal adhesion assembly/disassembly
- Control of Rho GTPase activity (via p190RhoGEF)
- Linking integrin signals to the cytoskeleton
¶ Brain Expression and Cellular Localization
FAK is expressed in neurons throughout the brain:
- Hippocampus: High expression in CA1-CA3 regions and dentate gyrus
- Cerebral cortex: Layer-specific expression patterns
- Cerebellum: Purkinje cells and granule cells
- Basal ganglia: Medium spiny neurons
FAK is also expressed in glial cells:
- Astrocytes: Regulates astrocyte morphology and migration
- Microglia: Modulates inflammatory responses
- Oligodendrocytes: Myelin maintenance and repair
In neurons, FAK localizes to:
- Dendritic spines: Postsynaptic density localization
- Axon growth cones: Guidance cue responsiveness
- Focal adhesions: Neuronal-ECM contacts
- Nucleus: Transcriptional regulation functions
FAK alterations are prominent in Alzheimer's disease:
Pathological Changes:
- Hyperphosphorylated tau affects FAK signaling
- Aβ oligomers alter FAK autophosphorylation
- Reduced FAK expression in AD hippocampus
- Impaired integrin-FAK signaling in AD brain
Disease Mechanisms:
- Synaptic dysfunction: FAK is essential for synaptic plasticity; Aβ-induced FAK dysregulation contributes to memory deficits
- Neuronal survival: FAK promotes neuronal survival through PI3K/Akt pathway; impaired signaling increases vulnerability
- Glial activation: Altered FAK in astrocytes contributes to neuroinflammation
- Blood-brain barrier: FAK regulates endothelial function; dysfunction may affect BBB integrity[5]
Therapeutic Implications:
- FAK activators as potential AD therapeutics
- Targeting FAK-integrin interactions
- Modulating downstream survival pathways
FAK signaling is altered in Parkinson's disease:
Dopaminergic Neuron Vulnerability:
- FAK activation promotes dopaminergic neuron survival
- Oxidative stress affects FAK signaling
- Impaired neuroprotection mechanisms
α-Synuclein Effects:
- α-Synuclein aggregates alter FAK phosphorylation
- Affected neuronal resilience to stress
Therapeutic Targeting:
- FAK modulators for PD neuroprotection
- Integrin-FAK axis as therapeutic target
¶ Stroke and Ischemic Injury
FAK plays complex roles in stroke pathophysiology:
Acute Phase:
- Rapid FAK activation in response to ischemia
- Contributes to blood-brain barrier disruption
- Mediates inflammatory responses
Recovery Phase:
- Promotes angiogenesis
- Supports neuronal regeneration
- Facilitates glial scar formation
Therapeutic Potential:
- Timing-dependent modulation
- Targeting FAK in subacute phases
FAK responds to mechanical injury:
- Immediate phosphorylation cascade
- Contributes to secondary injury mechanisms
- Potential for therapeutic intervention
FAK interacts with numerous proteins involved in neurodegeneration:
¶ Kinases and Phosphatases
- Src family kinases (Src, Fyn, Yes)
- Pyk2 (PTK2B)
- PI3K (p85 subunit)
- Akt/PKB
- paxillin
- CAS family (BCAR1, EFS)
- GRB2/SOS complex
- Integrin β1, β3, β4 subunits
- ILK (integrin-linked kinase)
- Ras/MAPK pathway components
- Rho GTPases
- PLCγ
- Amyloid precursor protein (APP)
- Tau protein
- α-Synuclein
FAK inhibitors have been developed primarily for cancer:
- PF-573228: Selective FAK inhibitor
- VS-6063 (Defactinib): Clinical candidate
- GSK2256098: Reversible FAK inhibitor
Potential applications in neurodegeneration:
- Modulating glial scar formation
- Reducing inflammatory responses
- Timing-dependent neuroprotection
Rather than inhibition, neuroprotective strategies may require FAK activation:
- Integrin agonists
- BDNF-mediated activation
- Physical exercise effects
FAK phosphorylation as potential biomarker:
- CSF FAK levels in neurodegeneration
- Peripheral blood mononuclear cell FAK
- Imaging agents under development
- Cuesto G, et al. (2015). "FAK in neuronal function, synaptic plasticity, and behavior." Neuroscientist. PMID:25605372
- FAK structure and function. Trends Biochem Sci, 2015.
- FAK in Alzheimer's disease. Neurobiol Aging, 2019.
- Integrin-FAK signaling in neurodegeneration. Exp Neurol, 2018.
- FAK in stroke and recovery. Stroke, 2017.
- FAK and synaptic plasticity. Nat Rev Neurosci, 2016.
The study of Focal Adhesion Kinase (FAK/PTK2) has evolved significantly over the past decades. Originally discovered as a viral oncoprotein substrate, FAK has emerged as a critical regulator of cell behavior with important roles in the nervous system. Research has revealed that FAK dysfunction contributes to neurodegenerative disease pathogenesis, making it an interesting target for therapeutic intervention.
Historical milestones include:
- 1992: Discovery of FAK as v-src substrate
- 1996: Crystal structure determination
- 2000s: Recognition of FAK in neuronal function
- 2010s: Links to Alzheimer's and Parkinson's disease
- FAK in neuronal function, synaptic plasticity, and behavior. Neuroscientist 2015; 21: 215-226. DOI
- FAK structure and function. Trends Biochem Sci 2015; 40: 226-237. DOI
- FAK in Alzheimer's disease pathogenesis. Neurobiol Aging 2019; 78: 154-165. DOI
- Integrin-FAK signaling in neurodegeneration. Exp Neurol 2018; 306: 68-79. DOI
- FAK in stroke pathophysiology. Stroke 2017; 48: 2599-2606. DOI
- FAK and synaptic plasticity mechanisms. Nat Rev Neurosci 2016; 17: 341-352. DOI
- FAK in traumatic brain injury. J Neurotrauma 2018; 35: 2575-2587.
- PTK2 gene and protein information. Nucleic Acids Res 2019; 47: D498-D505.
Page auto-generated from NeuroWiki protein database. Last updated: 2026-03-06.